HIV Antibody Test

HIV antibody testing is used to determine whether or not a person is infected with HIV. There is no cure, but early treatment of HIV infection and immune system monitoring can greatly improve long-term health. Also, knowing your HIV status may help you change your behaviour so that you and others are not put at risk

Antibodies to HIV can be detected by a screening test called an ELISA. The ELISA method is very sensitive but requires another test, a Western Blot, to confirm the results because false positives can occur. The antibody test is usually done in combination with a test called the p24 antigen test that detects the presence of the virus itself in blood or body fluids. If exposure to the risk of infection is recent, the p24 test becomes positive before the HIV antibody test. It then becomes negative when sufficient antibodies that bind HIV have been produced.

Antibody testing for HIV should be requested if you think you may have been exposed to HIV. Testing is recommended if:

• You are sexually active (three or more sexual partners in the last 12 months).
• You received a blood transfusion before 1985, or a sexual partner received a transfusion and later tested positive for HIV. (Since 1985 all blood donated in the UK and the US is tested for HIV, and infection by transfusion is now highly unusual.)
• You are uncertain about your partner's sexual behaviour with others.
• You are a male who has had sex with another male.
• You have used street drugs by injection, especially when sharing needles or other equipment.
• You have a sexually transmitted disease (STD).
• You are a health care worker with direct exposure to blood at work.
• You are pregnant. (There are now treatments that can greatly reduce the risk that a pregnant woman who has HIV will give the virus to her baby.)
• You are a woman who wants to make sure you are not infected with HIV before becoming pregnant.

In the UK the HIV test is free and anonymous. You can be tested by your doctor, at any clinic dealing with STDs such as Genito-Urinary Medicine (GUM) clinics, at Terrence Higgins Trust Fastest centres, at antenatal clinics, or at termination of pregnancy or drug dependency centres. Test results should not take longer than three days.

Point of care testing using a finger prick test can give a result in a few minutes. However, these tests can give false negative as well as false positive results. Positives should always be confirmed with tests on blood taken from a vein.

Your doctor is not informed of the clinic result without your permission. Your doctor or clinic staff will give advice about informing sexual partners if your test is positive.

You must have a test if you want to become a blood donor, use your sperm for artificial insemination, have an egg implantation or adopt a child.

A healthy individual has no antibodies to HIV. If you test positive for HIV antibodies on both the ELISA and the Western Blot tests, you are considered to be infected with HIV.

Antibody testing will not detect HIV immediately after exposure, during the window before the development of antibodies. (A p24 antigen test may be positive during this period.) Your result may be negative despite the fact that you are infected - a false negative result. Because of this, repeat testing is important. You should have another HIV antibody test at least three months from the time of a possible exposure to the virus.